Coaptive electrothermal tissue fusion or sealing involves the application of force and electrical energy to heat compressed tissue sufficiently to join together separate pieces of tissue. Electrothermal tissue fusion avoids the need to manually suture or tie-off tissues or vessels during a surgical procedure. The tissue is fused or sealed to prevent blood or other fluid loss so that thereafter the tissue may be cut or incised. Thus, the usual purpose of sealing or fusing tissue is to allow cutting of the tissue adjacent to the fused area during the surgical procedure.
In most cases, sealing the tissue and thereafter cutting the tissue adjacent to the sealed area is a desired and efficient way to perform a surgical procedure. Tissue cutting has therefore been combined with electrosurgical tissue fusion, in order to obtain efficiency and convenience. However, the tissue cutting is almost universally accomplished by use of a blade or other mechanical cutter rather than by cutting through the application of electrosurgical energy. The common types of mechanical tissue cutting devices have had the effect of compromising the effectiveness of the tissue seal or fusion. Without adequate tissue sealing or fusion, tissue cutting becomes substantially irrelevant because a failure to adequately seal or fuse the tissue offers no advantage over the typical manual procedures of suturing or tying off vessels or cutting tissue with a scalpel. Therefore, achieving and maintaining effective and reliable tissue fusion is a prerequisite to tissue cutting.
Although the exact details of the physical chemistry involved in tissue fusion are probably not completely understood, it is believed that the heat denatures chains or strands of tissue proteins in the separate pieces of tissue and the pressure causes the denatured protein chains to reconstitute or re-nature across the interface between the tissue pieces. The reconstituted proteins chains interact and intertwine with one another to hold the previously-separate tissues pieces together.
Collagen is one type of protein chain that appears to play an important role in tissue fusion. Collagen, also known as tropocollagen, consists of three polypeptide protein chains that form a triple helix. These protein chains are grouped or tangled together to establish significant tissue structure and strength, as is observed in blood vessels and ligaments. Applying heat to the tissue to raise the temperature to about 60-70° C. causes the protein chains to become disordered, disassociated, separated and untangled from the triple helix.
Elastin is another type of protein chain that appears to play an important role in tissue fusion. Elastin a collection of polypeptide protein chains that are individually and randomly cross-linked with each other to form a fibril. Fibrils are grouped or tangled together to form an elastin fiber. Upon the application of heat to raise the temperature to about 120° C., the elastin fiber becomes disassociated into a disordered collection of individual polypeptide chains, fibrils and fibers.
The heat which causes denaturation of the collagen and elastin chains also appears to create unfavorable molecular interactions among the components of the denatured proteins, resulting in a relatively high free energy state. Atoms with the same electrostatic charge, and hydrophobic and hydrophillic regions of the protein chains, begin to interact and create repulsive forces. Force must be applied at the interface between the tissue pieces during fusion to overcome the repulsive forces and to achieve more favorable interactions of the proteins chains thereby reducing the amount of free energy. Force must also be applied at the interface to maintain the denatured protein chains in physical proximity with each other so that they will reconstitute and join the tissue pieces together.
Although this theoretical model of tissue fusion is understandable, reliable tissue fusion is difficult to achieve on a consistent basis. Fusing blood vessels is of particular concern, because vessel fusion during a surgical procedure is the primary use of tissue fusion at the present time. Fused blood vessels that fail or leak after the conclusion of surgery lead to internal bleeding. Internal bleeding usually requires a second operation to gain access to and seal the leaking vessel, which induces further trauma and risk to the patient.
One prior art type of electrosurgical tissue fusion involves bipolar electrosurgery. The tissues are compressed between two jaws of a forceps-type instrument. The jaws also serve as electrodes to conduct high-voltage radio frequency (RF) current through the compressed tissue. Heat is generated from the RF current flowing through the resistance or impedance of the tissue, and that heat denatures the chains of protein.
Certain difficulties arise when using bipolar electrosurgical tissue fusion. The voltage between the jaws which compress the tissue and serve as electrodes is typically several thousand volts. The distance between the jaws is relatively small when the tissue is compressed. The relatively high voltage can create arcs which jump the small distance between the jaws and penetrate the tissue adjacent to the jaws, particularly toward the end of the fusion procedure when the tissue between the jaws dehydrates and its impedance increases. The arcs enter the tissue in minuscule spots and destroy or weaken the tissue at those spots. Under conditions of prolonged application of RF power in this manner, which is typical with bipolar electrosurgical tissue fusion, the arcing can actually perforate the tissue adjacent to the fused area, thereby rupturing the tissue and destroying any sealing effect from the sealed area if there are a significant number of ruptures. This is particularly the case when sealing vessels, because a typical failure mode of vessels sealed with bipolar electrosurgery is a leak or rupture in the wall of the vessel adjacent to the sealed area.
The RF current inherently flows through the tissue in a somewhat random or uncontrollable pattern depending on the point-to-point characteristics of the tissue and many other factors. As a consequence, uniform heating of the tissue is impossible to control. The non-homogeneous distribution of heat over the area to be fused causes the protein chains to denature and reconstitute in a variable and nonuniform manner. The nonuniform denaturation and reconstitution leads to fused tissue areas of variable, nonuniform and somewhat unpredictable strength.
Assessing when to stop the delivery of RF current during bipolar electrosurgical tissue fusion is difficult. Applying either too much or too little RF current leads to seals that are more likely to fail. The application of too much RF current creates an excessive amount of heat which drives chemical reactions that appear to oxidize or burn the tissue and change the nature of the protein chains, thereby diminishing their ability to reconstitute and create effective seals. Overly-heated tissue at the sealed area or adjacent to the sealed area increases the probability of a failure because the tissue has become brittle and lacks pliability due to excessive dehydration, thereby contributing to cracking and breaking. In contrast, prematurely stopping the delivery of RF current prevents an adequate amount of denaturing of the protein chains which, in turn, prevents an adequate amount of reconstitution of the proteins chains, thereby diminishing the strength of the seal.
Control systems have been developed to attempt to address the problem of applying too much or too little RF power during bipolar electrosurgical tissue fusion. Such control systems monitor some event associated with the application of electrical power to the tissue, typically the impedance. Monitoring the tissue impedance is based on an expectation that some change indicates the occurrence of appropriate sealing conditions. However, it is believed that no reliable relationship exists between tissue impedance and the formation of a consistently reliable seal.
Another problem with bipolar electrosurgical tissue fusion is that the alternating aspects of the RF electrical energy inherently results in less energy application per unit of time. The alternating aspects of the RF energy application is by nature a pulsed or alternating current (AC) energy application, as opposed to a continual energy application. The tissue must withstand relatively high voltages, but the amount of power transferred is not commensurate with the high voltage due to the pulsed or AC application of the RF current. The effect of the pulsed or alternating RF energy application is that more time is required to transfer an equivalent amount of energy compared to the transfer of energy delivered at a sustained peak value. The typical maximum power delivery with a widely used RF tissue fusion device is approximately 115 to 350 Watts per square inch (18-54 W/cm2).
Electrothermal instruments have also been used for tissue fusion. Electrothermal instruments have heating elements within jaws that grip and compress the tissue. Electrical current is conducted through the heating elements to generate the heat that is applied to the compressed tissue. As with bipolar electrosurgery, previous electrothermal instruments have produced varying and inconsistent tissue fusion results, possibly as a result of an ineffective control system or control functionality based on misperceptions relating to tissue fusion physiology, including the perceived limitation of not heating the tissue above the 120° C. point where elastin protein chains denature. The prevalent view is to avoid elevating the temperature of the tissue beyond the 120° C. point where elastin protein chains denature, because it is believed that temperatures beyond that point are destructive to the proteins chains. Consequently, all presently known tissue fusion technologies attempt to limit the tissue temperature to no more than approximately 120° C., and many tissue fusion technologies limit the temperature of the tissue to approximately 100° C. to avoid creating steam.
The typical approach used to combine tissue cutting and fusion is to incorporate a mechanical blade with the applicator of the RF or thermal energy. The electrodes of the RF applicator, or jaws of the electrothermal applicator, create the fusion. Once the fusion is complete, the blade is advanced in grooves or slots formed in the electrodes or jaws to sever the fused area of the tissue, usually while the electrodes or jaws maintain pressure on the tissue. Such mechanical cutting systems are prone to sticking or jamming. Usually the mechanical blade is relatively thin and therefore has a tendency to distort while cutting, which may cause friction and sticking as it advances in the grooves or slots. The fluid and small pieces of tissue at the surgical site may also interfere with the intended movement of the mechanical blade.
The mechanical action of the blade severing the fused area of tissue also has the tendency to induce forces on the sealed area and the adjacent tissue, which typically compromises the effectiveness of the seal. Advancing the mechanical blade through the sealed area can separate the sealed area sufficiently to create a fluid leak and may even crack or otherwise destroy the sealed area to create a fluid leak. In certain circumstances, the mechanical blade can become so stuck or jammed to prevent release of the tissue from between the electrodes or jaws. Such a circumstance is particularly serious in minimally invasive (endoscopic or laparoscopic) surgery because the closed minimally invasive procedure has to be converted to an open surgical procedure to gain access to the stuck applicator and release it from the tissue. Converting a closed minimally invasive surgical procedure to an open procedure induces substantial unexpected trauma on a patient, and unexpectedly prolongs the duration and risk associated with the surgical procedure.
A further disadvantage of mechanical cutting is that the blade must be advanced in a linear direction, making it impossible to cut on a curve. Many surgeons prefer to use instruments which are curved, particularly in minimally invasive procedures where visualization is difficult because of a lack of stereoscopic vision. A curved electrode or jaw is easier to observe from the monoscopic perspective of minimally invasive surgical procedures.
Attempts have been made to electrothermally cut tissue simultaneously while fusing the tissue, but all such known attempts have proved unsuccessful or impractical. In general, tissue cutting while simultaneously fusing the tissue has involved delivering energy into the tissue for a considerable length of time. The prolonged energy delivery has apparently heated the tissue to the point where essentially complete dehydration of the tissue occurs and causes the tissue to become crisp, brittle and friable, like a potato chip. The tissue simply reaches a point where the sealed area disintegrates or crumbles.
Such prolonged heating has the effect of inducing thermal spread into the adjacent tissue, which compromises the strength of the seal and the unsealed adjacent tissue areas. The brittleness of the tissue causes it to separate or crack in a non-defined or non-controllable manner, which may extend the crack to the adjacent tissue walls and compromise or destroy the seal and create a leak. Moreover, the separation through the sealed area is essentially non-defined because of the relatively large area of total dehydration and the inability to control where the dehydrated tissue will crack or disintegrate. Consequently, known tissue fusion and simultaneous cutting procedures result in cutting which is more of the nature of ill-defined tissue obliteration rather than linear cutting along a desired path which surgeons prefer in order to avoid damaging more tissue than is necessary during the overall surgical procedure.
Although the principal concern of tissue fusion and cutting in a single procedure is creating reliable seals that hold on a long-term basis, another very important practical consideration is an ability to create the seal and perform the cut quickly. A typical surgical procedure will involve sealing many blood vessels at the surgical site. The typical time required by known electrosurgical tissue sealing devices to create a single seal is about 5-12 seconds. When also simultaneously electrothermally cutting the tissue in the manner described, the entire energy application extends from 30 to 60 seconds. When mechanically cutting the tissue after it has been fused, an additional 5 to 10 seconds is required in order to advance the mechanical blade through the fused area, providing that no sticking or jamming occurs. A considerable amount of time is therefore consumed in making each single-procedure seal and cut. Considering that a typical surgical procedure may require sealing and cutting scores of vessels, a considerable amount of the total overall surgical procedure time is consumed by vessel sealing and cutting.
Moreover, because of concern about the reliability of the vessel seals, the typical practice is to create two sequential seals at each severed end of the vessel. The theory is that if the first or upstream seal fails, the second or downstream seal becomes a redundant backup to prevent fluid leakage. The time to create the primary and backup seals is more than twice the amount of time required to create a single seal when the time for repositioning and observing the quality of each seal is taken into account. Further still, double seals must be made at both ends of each severed vessel if there is concern about leaking from the seals created at opposite ends of the vessel which is cut. Thus, a considerable amount of time is consumed during the surgical procedure by sealing vessels and cutting them. The time consumed by cutting and sealing vessels extends the time required to accomplish the entire surgical procedure, or alternatively, detracts from the time available to accomplish other activities during the surgical procedure.